1. read the manual pages in book form.

2. play a man page quiz with a friend: - read a random command and ask for the description - read a random description and ask which command it is for.

I've done both as an undergraduate. The HP-UX manual set remain on the shelves right next to me. Over the years, I found letting candidates compose a pipeline of commands to solve a problem is a great way to make interviews more fun ("How would you solve this problem without writing a program, by combining existing ones?").